1. Field of the Invention
The present invention relates to an imaging apparatus, and more particularly, to an imaging apparatus and an image signal processing method thereof providing a wide dynamic range.
2. Description of the Related Art
The human eye has a dynamic range of approximately 120 dB. The dynamic range is a visible range of sight imaging from dark regions to light regions visible to the human eye. However, in general artificial signal processing techniques utilized by an imaging apparatus such as a digital camera adopting a charge coupled device (CCD), the generated images exhibit a range of only approximately 60 dB. Ongoing research into signal processing methods has therefore been conducted, with the goal of widening the dynamic range.
Also, when an image signal is displayed in the monitor of a camera, the dark regions in a low-luminance image are often displayed darker than the luminescence of an actual imaged dark object. In order to compensate for this phenomenon, a gamma correction method is employed for lightening the extreme dark region by amplifying low-luminance portions of the image according to a predetermined gain.
However, in the conventional gamma correction technique, because the signal-to-noise ratio (S/N ratio) in a low-luminance image is often very low, image sensitivity therefore decreases to a extremely low level following amplification. Also, a digitally-quantized value generated from the analog image signal, is converted with a high conversion rate, thereby increasing quantization noise and increasing lumping in the output image. Display of color is likewise adversely affected by the conventional correction process.
Therefore, in the conventional gamma correction technique, dynamic range is limited, low-luminance image sensitivity is decreased, and color display is inaccurate.